Dosimetric characterization of a synthetic single crystal diamond detector in a clinical 62 MeV ocular therapy proton beam

Abstract

a b s t r a c tA synthetic single crystal diamond based Schottky photodiode was tested at INFN-LNS on the proton beam line (62 MeV) dedicated to the radiation treatment of ocular disease. The diamond detector response was studied in terms of pre-irradiation dose, linearity with dose and dose rate, and angular dependence. Depth dose curves were measured for the 62 MeV pristine proton beam and for three unmodulated range-shifted proton beams; furthermore, the spread-out Bragg peak was measured for a modulated therapeutic proton beam. Beam parameters, recommended by the ICRU report 78, were evaluated to analyze depth-dose curves from diamond detector. Measured dose distributions were compared with the corresponding dose distributions acquired with reference plane-parallel ionization chambers. Field size dependence of the output factor (dose per monitor unit) in a therapeutic modulated proton beam was measured with the diamond detector over the range of ocular proton therapy collimator diameters (5-30 mm). Output factors measured with the diamond detector were compared to the ones by a Markus ionization chamber, a Scanditronix Hi-p Si stereotactic diode and a radiochromic EBT2 film. Signal stability within 0.5% was demonstrated for the diamond detector with no need of any pre-irradiation dose. Dose and dose rate dependence of the diamond response was measured: deviations from linearity resulted to be within 70.5% over the investigated ranges of 0.5-40.0 Gy and 0.3-30.0 Gy/min respectively. Output factors from diamond detector measured with the smallest collimator (5 mm in diameter) showed a maximum deviation of about 3% with respect to the high resolution radiochromic EBT2 film. Depth-dose curves measured by diamond for unmodulated and modulated beams were in good agreement with those from the reference plane-parallel Markus chamber, with relative differences lower than 7 1% in peak-to-plateau ratios, well within experimental uncertainties. A 2.5% variation in diamond detector response was observed in angular dependence measurements carried-out by varying the proton beam incidence angle in the polar direction. The dosimetric characterization of the tested synthetic single crystal diamond detector clearly indicates its suitability for relative dosimetry in ocular therapy proton beams, with no need of any correction factors accounting for dose rate and linear energy transfer dependence.

Response of synthetic diamond detectors in proton, carbon, and oxygen ion beams

“…LET‐value increases upto ~20 keV/μm, at the depth corresponding to the range 80%. As expected, results confirm the LET‐independent response observed in previous experimental work . Considering the uncertainties of the results, a LET dependence of the microDiamond detectors is not measurable and we conclude that there is agreement between the normalized response of the microDiamond detectors and the normalized response of Markus ionization chamber.…”

“…In photon, electron and proton beams, this detector is described as suitable for small field dosimetry . Also in protons, most dosimetry studies conclude that the response of the PTW‐60019 microDiamond detector exhibits no LET dependence nor quenching effect (Mandapaka et al, Marinelli et al, Yuichi et al, Rossomme et al, Akino et al). In, which is based on an intercomparison of four microDiamond detectors in a clinical 138 MeV proton beam, authors reported a nonreproducibility between devices in terms of stability, sensitivity, and LET dependence.…”

Implementation of dosimetry equipment and phantoms at the MedAustron light ion beam therapy facility

“…In our evaluation, dose differences were lower than 1% at all depths and suggest that our diamond detector did not evidence any quenching issues for protons (Fig. ), but for full characterization of the detector additional work would be required …”

“…, the evaluation of four microDiamonds indicates that the microDiamond detectors are not reproducible and presented differences in terms of stability, sensitivity, and LET dependence. The LET dependence is in contrast with other studies . Evaluation of the LET dependence in scanned ion beams is rather time consuming compared to scattered beams, since the beam must be scanned and the depth‐dose curve must be acquired point‐by‐point.…”

“…In some cases, quenching effects may occur in regions with increased LET and therefore solid detectors must be used carefully. Diamond detectors are tissue equivalent and therefore could be of high interest in future . The microDiamond TM60019 (PTW, Freiburg), which offers an effective thickness of 1 μ m, a radius of 1.1 mm and a volume of 0.004 mm 3 , has been used for reference transverse profile acquisitions in water for TPS commissioning.…”